1. Field of the Invention
The present invention relates to multi-band antennas, and more particularly to a dipole multi-band antenna usable with wireless communications.
2. Description of the Prior Art
Four standards used in Wireless Local Area Network (WLAN) include IEEE 802.11, IEEE 802.11b, and Bluetooth in the 2.4 GHz frequency band, and IEEE 802.11a in the 5 GHz frequency band. When electronic equipment must communicate in more than one frequency band, antennas must be designed which communicate in more than one band and which meet the relevant standards. A conventional antenna is disclosed in China Pat. Application No. 01,224,549 (shown in FIG. 5 of the China Application). The antenna includes a substrate, with an upper metal layer and a lower metal layer printed on two opposite surfaces of the substrate. The upper metal layer includes a signal fed microstrip and a one-quarter-wavelength radiation portion extending from one end of the microstrip. The lower metal layer includes a grounding plane and a pair of one-quarter-wavelength radiation portions extending from the grounding plane. Signals are fed into the microstrip. The three one-quarter-wavelength radiation portions work together as a dipole. This antenna can be used in mobile phones, WLANs and other wireless communication devices. However, this antenna only works in one frequency band.
China Patent Application No. 98,126,980 discloses an antenna operable in more than one frequency band. The antenna includes a substrate, an upper and a lower metal layers printed on two opposite surfaces of the substrate, two conductive strips printed on one lateral side of the substrate and connecting the upper and lower metal layers together, and a feeder device connecting to the two conductive strips and to a middle finger of the upper metal layer. The upper metal layer has two pairs of side portions formed symmetrically about the middle finger. Each pair of side portion responds to a different frequency band. However, the substrate is very thin, so the two conductive strips occupy a relatively small area, which increases the difficulty of connecting them to the feeder device. The cost of manufacture is thus increased. Additionally, the location of the two conductive strips on the lateral side of the substrate is restrictive, so the layout of the antenna lacks flexibility.